This invention relates generally to the field of oil deflector seals for rotating shafts, and more particularly to an oil deflector system including a seal that reduces gas flow around a rotating shaft to prevent ingestion of moisture and contaminates into a bearing lube oil system.
At least some known large steam turbines experience dirt and moisture contamination of the bearing lubricating oil system. Such contamination, if not corrected, may negatively impact bearing performance as well as systems that interface with the lube oil system such as, but not limited to control systems. Fossil-fueled steam turbines are particularly subject to the problem since they frequently operate in an environment contaminated with coal dust and fly ash.
One path of entry of the contaminants into the lubricating oil system may be by being drawn in through the bearing oil seals along with the atmospheric air that is necessary for ventilation of the system oil tank and for oil seal cooling. The bearing oil seals, commonly referred to as oil deflectors, are labyrinth seal arrangements which prevent leakage of lubricating oil from the associated bearing. Contaminated air is drawn in through the seal by the lubricating oil system vacuum, entering through the clearances formed by the oil deflector rings (teeth) and the shaft. Such contaminant ingestion may clog the deflector teeth and in some cases, the dirt build-up has been carbonized by high temperatures resulting in shaft damage.
A known attempt to prevent such effects off contamination includes supplying a pressurized gaseous fluid to the seal labyrinth seals. For example, steam seal systems, compressors, and other rotating equipment have been fitted with seals adapted to receive (and sometimes extract) a pressurized gas. These devices usually contain multiple cavities located along the shaft and use relatively small passages provided in the seal housing, or cavities, to inject the fluid into the tooth area. Because of the high air injection velocities for these configurations, high pressure and correspondingly high flow horsepower are needed to seal around the shaft. However, the close clearances eventually open reducing the effectiveness of the seal and the additional equipment also requires periodic maintenance attention.